Yours is a very strange situation. Generally plug-n-play ps/2 keyboards and also USB ones should function during the boot sequence since they don't need any additional software to run. If possible try to get a usb keyboard and try to use that. It should work. Even if it does, I strongly recommend u call an authorised technician and fix the problem permanently. I presume that your desktop is under warranty.

I have similar situation on old PIII system with new PS/2 keyboards. Any pressed key did not send signal to keyboard portal and not give answer (char typing on the screen). But Linux is not the reason for it, but the old hardware the only.
Then I found an old keyboard (~2000-th year) and it began to work, but slowly a little, the delay is required between key pressings.